There is a need to mark certain items to avoid counterfeiting. Marked items can be monetary tools such as banknotes, stamps, checks etc or government documents such as passports, visas etc. They can also be high value commercial items. Sometimes the authenticated items are pharmaceutical, to protect not only the monetary value but also the safety of the users. Most systems need to be verified by machine reading, sometimes through a wrapper or enclosure. One class of solutions uses a small amount of an additive, known as a taggant. The taggant can be detected with a specialized detector but is not visible under normal conditions. The advantage of a taggant is, besides being covert, is that it can be made machine-readable at high speeds. At very small doses it can be very difficult to find and identify, unless the specialized detector is used. The disadvantage of tagging is that it can carry a limited number of combinations, particularly if it has to be machine-readable. This does not allow giving each item a unique identification code or secure serial number (the visible serial number or barcode printed on most items can be easily counterfeit). To make it harder to counterfeit some systems use a random distribution of fibers or patterns, but because they rely on simple optical scanning for reading, a simple photocopy of the image will also read as genuine in most cases.